Wind forces on structures are usually schematized by the sum of their mean static part and a nil mean fluctuation generally treated as a stationary process randomly varying in space and time. The multi-dimensional nature of such a process gives rise to relevant numerical efforts in order to carry out the dynamic analysis of the structural response. With the aim of drastically reducing the above computational burden, this paper introduces a method by means of which the external fluctuating forces are schematized by an equivalent identically coherent process, rather than by the actual cross-correlated process. This process is identified by a power spectral density function, called the Equivalent Wind Loading Spectrum, whose expression is given in closed form.